class_docstr: Handles tokenization history.
docstr: Override from parent class to possibly add [SEP] token.
docstr_tok: ["Override","from","parent","class","to","possibly","add","[","SEP","]","token","."]
code: def get_history_vec(self):
      """
      Override from parent class to possibly add [SEP] token.
      """
      if not self.sep_last_utt or len(self.history_vecs) <= 1:
          return super().get_history_vec()
  
      history = deque(maxlen=self.max_len)
      for vec in self.history_vecs[:-1]:
          history.extend(vec)
          history.extend(self.delimiter_tok)
      history.extend([self.dict.end_idx])  # add [SEP] token
      history.extend(self.history_vecs[-1])
  
      return history
  
imports: import os
  from collections import deque
  from typing import Optional
  import torch
  from parlai.agents.bert_ranker.bert_dictionary import BertDictionaryAgent
  from parlai.agents.bert_ranker.helpers import BertWrapper, MODEL_PATH
  from parlai.core.opt import Opt
  from parlai.core.params import ParlaiParser
  from parlai.core.torch_agent import History
  from parlai.core.torch_classifier_agent import TorchClassifierAgent
  from parlai.utils.io import PathManager
  from parlai.utils.misc import warn_once
  from parlai.zoo.bert.build import download
label_desc: Use image node_id 2 for calling the BertClassifierHistory obj's underlying member method code with example usage: obj.get_history_vec() and returns: history, super